The objectives of this research program are to study the basic biological processes and mechanisms involved in the control of the fibrinolytic system in health and disease. These studies involve the plasma protein plasminogen, its mechanism of activation, the preparation of different plasmin forms, and plasmin-derived heavy(A) and light (B) chains, including a functionally-active light (B) chain. Studies will be carried out on the preparation of a functionally-active recombinant plasmin from isolated homologous and heterologous chains. Studies on the molecular interaction of plasminogen, plasmin, and the functionally-active light (B) chain with streptokinase are being carried out to determine the nature of the binding site(s), and the definition of the catalytic efficiency of the activator function. The enzymatic properties and plasminogen activator activities of these complexes are being studied for the purpose of developing new, and more efficient and effective, activators. Studies on the biological half-life of these activators in an experimental animal model will be carried out. Studies will be carried out on the functionally-active light (B) chain, and attempts will be made to crystallize the molecule. Also, a functionally-active zymogen (plasminogen with an active site) will be prepared in order to study its enzymatic and biological properties. Quantitative methods have been developed for determining the catalytic efficiency of plasminogen activators in steady state kinetic studies using synthetic substrates. These methods sould permit use to study the components of the fibrinolytic system in plasma and to look for genetic abnormalities of plasminogen. Another study will involve the biosynthetic mechanisms for plasminogen production in mammalian liver. These types of studies will permit us also to develop phylogenetic relationships between the different species. Methods will be developed for preparing recombinant plasmins from the functionally-active plasmin-derived light (B) chain and the noncatalytic chains from several blood coagulation factors. These studies may permit us to prepare hybrid enzymes and to establish a function for the plasmin heavy (A) chain.